QST TECHNIQUE

Why QST?

What is QST?

Quantitative Sensory Testing (QST) is a valuable method for diagnosing peripheral nervous system disorders, including chronic pain and pain related to various diseases, such as Diabetes and CRPS. QST essentially determines the sensation and pain thresholds for cold and warm temperatures, and the vibration sensation threshold by stimulating the skin and comparing the results to normative values built in the software. When the stimulus activates stimuli-specific receptors; the nerve fibers that innervate the receptors communicate the stimuli message to the central nervous system, where feeling occurs.

Quantitative Sensory Testing is a non-invasive, pain-free technique that can assist in early detection, therapy selection and monitoring the progression and recovery of patients with peripheral sensory disorders.

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The diagnostic power of Quantitative Sensory Testing as a tool in diagnosing peripheral nervous systems disorders is a unique combination of instrumentation and technology, integrated with robust software and mission-specific hardware. When packaged in application-specific systems and configurations based on varying sensory modalities, and different body locations for specific medical or research needs, QST systems are valuable elements in medical research and treatment. This integration and packaging is the foundation of all Medoc’s products and systems.

How do our products work?

Medoc’s products are based on thermal (warm and cold) and vibratory stimulator technology. In the TSA-II – NeuroSensory Analyzer, a small probe, called a “thermode,” is attached to the patient’s skin. The device is capable of heating or cooling the skin, as needed. Technically, the thermode is based on Peltier elements. It consists of semiconductor junctions, which produce a temperature gradient between the upper and lower stimulator surfaces produced by the passage of an electric current.

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What are the available modalities?

The thermal sensory testing element measures the thresholds for four sensory sub-modalities:

Cold induced pain (CP), the most variable and difficult to assess of all previous modalities, at about 10º C (combination of both C and A-delta fiber mediated sensation)

Why vibration?

The VSA-3000 – Vibratory Sensory Analyzer complements the thermal tests and enables clinicians to test the large nerve fibers by measuring sensory thresholds for vibration. This is useful in early diagnosis, follow-up, and therapy assessment. For example, these thresholds deviate from the normal range in diabetic neuropathy and peripheral nerve diseases. The computerized device measures thresholds for vibratory stimuli at the range of 0-130 microns and at the rate of 0.1 to 4.0 microns/sec. The vibratory method provides two types of stimuli: stimuli that increase in intensity until a sensation is felt and stimuli that decrease in intensity until no sensation is felt (up or down modalities).

Advanced QST

Contact Heat Evoked Potential Stimulation (CHEPS)

PATHWAY model CHEPS technology is based on an advanced computerized thermal stimulator used to investigate human thermal and nociceptive pathways mediating sensory and pain perception. This selective stimulation and identification of A-Delta & C-fibers through EEG signal waveform recording uses a specially designed large probe (27 mm diameter) for evoking a stronger brain response. An EP can be produced by delivering extremely fast stimuli from baseline temperature to 55ºC in less than 250 milliseconds, due to the rapid rise in temperature (70ºC per second). This is made possible with the development of a new breakthrough heat-foil technology, combined with a solid-state thermoelectric cooler (Peltier elements) and powerful temperature-controlled algorithms that sample online temperature at a rate of 200 times per second. This technology is ushering in a new era in the field of objective documentation of evoked pain response.